The NACE Standard MR0175, particularly of January 1992 applies as a guideline to turbocompressors that compress gases containing hydrogen sulfide. The standard defines an operation range in which the gas being handled is at a total pressure of 65 psia (448 kPa) or greater and the partial pressure of hydrogen sulfide in the gas is greater than 0.05 psia (0.34 kPa). This guideline stipulates that the yield point of the material and consequently also the circumferential velocity of a compressor impeller must not exceed a set limit value if a combination of gas pressure and hydrogen sulfide concentration in the gas, which combination is specified in this guideline, is exceeded.
The gas composition is approximately the same in all impellers of the compressor. The pressure of the gas increases in each compressor impeller, and the final pressure is reached after the last impeller.
If the guideline is applied to any one impeller of a turbocompressor, all impellers of the compressor are designed according to this guideline in the known manner.
If the guideline is applied to all impellers of a turbocompressor, even though it does not apply, e.g., to the first impeller, all impellers of the turbocompressor have a set maximum circumferential velocity of, e.g., 260 m/sec.
Compressors of the applicant for "wet gases" and similar gases have been known with, e.g., three impellers arranged to the left in the direction of flow and three impellers arranged to the right in the direction of flow. The process gas to be compressed enters at the housing on the left, is compressed in the impellers on the left, first in the uncritical H.sub.2 S area, and then in the critical H.sub.2 S area, and is subjected to intermediate cooling outside the compressor. The process gas then enters the compressor on the right-hand side of the housing, is compressed on the right in the critical H.sub.2 S area, and it leaves the compressor in the middle.
The number of impellers on the compressor shaft on the left and right is determined by the external process conditions. The circumferential velocity of all impellers is below the maximum allowable circumferential velocity, which results from the yield point of the material of the impeller, which is lowered for the H.sub.2 S conditions.
If a defined pressure value is not exceeded according to such guideline at a defined percentage of hydrogen sulfide in the process gas, the contents of this guideline do not apply.